The multiple adhesive interactions between leukocytes and endothelial cells or extracellular matrix proteins are a key factor in the regulation of immunity and inflammation. The earliest events in the migration of leukocytes out of the vasculature at site of inflammation include leukocyte rolling followed by changes in integrin avidity, which lead to subsequent firm adhesion (for reviews see Butcher, Cell 67:1033-1036 (1991); Harlan, Blood 3:513-525 (1985); Hemler, Annu. Rev. Immunol. 8:365-400 (1990); Osborn, Cell 62:3-6 (1990); Shimizu et al., Immunol. Rev. 114:109-143 (1990); Springer, Nature 346:425-434 (1990); and Springer, Cell 76:301-314 (1994)). In response to chemotactic factors, the leukocytes migrate through two adjacent endothelial cells and into tissues that are composed, in part, of the extracellular matrix protein fibronectin (FN) (see Wayner et al., J. Cell Biol. 105:1873-1884 (1987)) and collagen (CN) (see Bornstein et al., Ann. Rev. Biochem. 49:957-1003 (1980); and Miller, Chemistry of the collagens and their distribution, in “Extracellular Matrix Biochemistry”, K. A. Piez and A. H. Reddi, editors, Elsevier, Amsterdam, 41-78 (1983)). Important recognition molecules that participate in these adhesive reactions belong to the integrin gene superfamily (for reviews see Hemler, Annu. Rev. Immunol. 8:365-400 (1990); Hynes, Cell 48:549-554 (1987); Shimizu et al., Immunol. Rev. 114:109-143 (1990); and Springer, Nature 346:425-434 (1990)).
Integrins are heterodimers composed of non-covalently associated subunits, referred to as the alpha (α) and beta (β) subunits. To date, 8 integrin β subunits have been identified which can associate with 16 distinct α subunits to form 23 distinct integrins.
The α4β1 integrin, also known as VLA-4 (Very Late Antigen-4), is constitutively expressed on the surface of leukocytes including lymphocytes, monocytes, eosinophils and basophils (see Hemler et al., J. Bio. Chem. 262:11478-11485 (1987); and Bochner et al., J. Exp. Med. 173:1553-1556 (1991)). VLA-4 is reported to be present on neutrophils from septic patients (see Ibbotson et al., Nature Med. 7:465-470 (2001)). VLA-4 binds to vascular cell adhesion molecule-1 (VCAM-1) on activated endothelial cells, resulting in extravasation of leukocytes (Elices et al., Cell 60:577-584 (1990)). Once the cells have reached the extravascular space, VLA-4 can bind to the connecting segment 1 (CS-1), an alternatively spliced region of the FN A chain (Wayne et al., J. Cell Biol. 109:1321-1330 (1989)). In addition, VLA-4 is known to bind to osteopontin, a protein upregulated in arteriosclerotic plaques (see Bayless et al., J. Cell Science 111:1165-1174 (1998)).